The present invention relates to a method of breaking foam as well as to an arrangement for breaking a foam.
More particularly, it relates to a method and an arrangement for breaking a foam, especially in installations of wet chemical treatment of printed circuit boards, with stations in which a treatment liquid is sprayed in a working plane onto a substrate to be treated and from where it is discharged into a supply tank located underneath.
During a wet chemical treatment of printed circuit boards process steps are utilized in which during the treatment of printed circuit boards a foam is produced. Such process steps are for example a stripping of a photoresist with alkali solutions, or the development of the resist.
The treatment of the printed circuit boards is in many cases performed in throughgoing installations, in which the boards are transported in a horizontal position through the treatment stations and between them. The liquid treatment chemicals are conventionally sprayed through nozzles onto the surfaces to be treated.
Pumps are utilized for transporting the treatment liquids. They aspirate the liquids from a supply tank which is located underneath the treatment plane, and transport the same to the nozzles. From the treatment plane, the liquid runs back to the supply tank.
During spraying of the liquid and its discharge back to the supply tank, the process can lead to the formation of a foam for example during the above mentioned treatment steps. The volume of the foam continuously increases with progressing duration of the treatment. Without measures for suppressing the foam formation, the foam discharges through the openings with which the supply tank communicates with the atmosphere. If all these openings were sealed, which would lead to considerable expenses, the foam would still escape through unavoidable openings in the treatment plane of the printed circuit boards.
All measures must be taken to eliminate or at least to reduce the foam formation. Conventionally for this purpose anti-foaming agents are added to the solution and prevent in a chemical manner the generation of the foam. The anti-foaming agents prevent or reduce the foam formation. However, they possess the disadvantage that they act in an unfavorable manner on the efficiency of the treatment solution. Also, with the increased time of the utilization of the treatment solution, an increased portion of the anti-foaming agents can be added, since the solution such as for example for stripping of photoresist always receives more organic components which cause the foam generation. These methods of foam suppression involve significant costs and their utilization is very expensive.